Page 2 of 3 FirstFirst 1 2 3 LastLast
Results 11 to 20 of 27

Thread: Another muffler exhaust question.

  1. #11
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    Thanks. I guess you can send me the muffler back. If you still have it around, that is. I'm kind of curious how it compares to the one I built, sound-wise. Due to the limitations of using pre-bent pipes, mine isn't exactly perfectly lined up either (tilted a little, one tail pipe is a little long, and it hangs a little low, but it gets the job done).

    -- Joe

  2. #12
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    Now that my car is finally on the road again, I did a crude test on how loud my exhaust is. I used a simple dB meter I got off of Amazon a while back, and was only standing about 15-20 feet behind the car while it was idling (already warmed up), pointing the meter right at the back of the car. I got just under 85 dB. Not bad. When standing in front of the car it's surprisingly quiet. I need to do something with more standard meter placement and distance at some point, once I figure out what that is...

    As mentioned before, the setup is DPI headers, off-the-shelf CARB-compliant cats, 2.5" pipes, and a Borla Pro XS dual in/dual out muffler. Unlike normal DMC mufflers, the Borla is designed with both inlets on one side and both outlets on the other side (although it's reversible, so it doesn't matter which side is which), so I can't just plug the inlets into the "top" and the outlets into the "bottom". To work around this, I have drivers side going in and out of the "top" of the muffler, while the passenger side goes through the "bottom". It sits low for a DeLorean muffler due to the pre-bent pipes and clamps. I'm also using heat shield wrap instead of a metal shield to keep the heat off the engine, just for simplicity.

    I did find what I'll describe as a "buzz" from the exhaust at >2000 RPM. This was just the right frequency to be annoying. To counter this, I installed two Car Chemistry three disc silencers in the pipes after the muffler, one on each side. I had welded the cap-with-a-hole on the muffler side of the silencers to bring it down a little bit. This mostly removed the buzz and made the car much more enjoyable to drive. I think it also dropped a few decibels -- not a lot, but it sounds quieter to me. I of course didn't think to do before-and-after sounds tests, so all I have is the after reading of 85 dB. At some point I'll probably drop the exhaust and install two other pipes between the cats and muffler that include two more CC inserts that have both caps welded on and stainless steel wool between the rings, which would probably lower the noise a few more decibels, but I'm not in a hurry to do that just yet.

    Overall, the sound is fine to me. It's not terribly low, but it's not very high either. It's not exactly quiet, but it's not super loud either -- it's diesel truck levels, or around what my wife's '72 Charge puts out (although that has a lower note than my exhaust setup). I don't remember what the stock or DPI exhausts sound like at this point, so I can't really compare them, and video always sounds different than real life, but I'll try to capture one this weekend.

    -- Joe

  3. #13
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    Some quick Googling found this document (it's for Australia, but other things I found seem to match), which suggests the meter be positioned about 1.64' (0.5m) way from the exhaust on a 45 degree angle (there's a diagram in the document), and revved at 3000 RPM. It also notes to make sure that there aren't any noise reflections by mounting the meter on a tripod, although I'll probably just stand to the side and hold it at arm's length.

    I'll try to get a measurement done this weekend, along with a video of the exhaust noise and note.

    -- Joe

  4. #14
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    So doing that test at 790 RPM warmed up yielded ~96 dBc. Not exactly what I’d call quiet. Maybe I will install that second set of silencers...

    Although apparently a lot of regulatory sound tests are done with the dBa filter, to dBc. Maybe I’ll hunt down one of those meters and try again.

    — Joe
    Last edited by jangell; 02-05-2019 at 11:16 PM.

  5. #15
    Senior Member vwdmc16's Avatar
    Join Date:  May 2011

    Location:  sacramento

    Posts:    1,341

    My VIN:    1768

    Club(s):   (NCDMC) (DCUK)

    Any scientific test been done to measure the Db of stock exhaust?

  6. #16
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    230

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by Dontilgon View Post
    I enjoy the sound of my stock exhaust but would like to update the design or clean up the engine compartment. Clearly all the newer aftermarket systems out there do this very nicely. The only problem I find with this new systems are they are bit noisy or drone. Does anyone have experience with an aftermarket quiet exhaust. Honestly if there was replacement headers that mounted to the stock exhaust , that would be the perfect solution for me. I have a test pipe and this was all the extra sound I enjoy. Also what is the deal with the wrap around exhaust design, seems a bit complex for an exhaust system. Thanks in advance
    I was concerned with drone noise in my car too. hesitant on what exhaust to buy. I ended up with DPIs Spec 1 and I love it. It doesn't seem to drone much at all, I can listen to the radio (craig) no issues. The headers go down and back so most heat is away from engine compartment. (getting rid of the cross over pipe was a huge improvement) little more performance is gained, and slightly more aggressive sound. all around a great exhaust and Josh stands by it too. ( I do however highly recommend replacing the bundle of brown wires from the alternator to the starter with a heavy battery cable, and securing it away from the headers.)

  7. #17
    Senior Member
    Join Date:  Nov 2014

    Location:  Northwest Florida

    Posts:    164

    Club(s):   (DCF)

    Quote Originally Posted by hippieman9 View Post
    I was concerned with drone noise in my car too. hesitant on what exhaust to buy. I ended up with DPIs Spec 1 and I love it. It doesn't seem to drone much at all, I can listen to the radio (craig) no issues. The headers go down and back so most heat is away from engine compartment. (getting rid of the cross over pipe was a huge improvement) little more performance is gained, and slightly more aggressive sound. all around a great exhaust and Josh stands by it too. ( I do however highly recommend replacing the bundle of brown wires from the alternator to the starter with a heavy battery cable, and securing it away from the headers.)
    I can vouch to this. I also changed mine for a SPEC 1 and the drone is significantly lower: a huge plus for me as a daily driver.

  8. #18
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    I did another test with a nice new dBa meter, and got 76 dBa at warm idle. This was standing about a foot and a half away at a 45 degree angle from the exhaust with the meter pointed at the exhaust.

    Also, I think I have an exhaust leak that seals itself when the car gets warm. Today was a medium-length highway trip, and when I got home the car was noticeably quieter than when I left. I'll be taking apart the exhaust in a couple of weeks and adding some sealer between the clamps to see if I can get it to be quiet (76 dBa) all the time at idle. I'll try to do some 3000 RPM tests after that's taken care of.

    Also, the grade of stainless steel for my exhaust may not be the best. The Borla Pro XS muffler seems fine, as do the DPI headers, but the stainless steel Walker catalytic converter already has a fair bit of surface rust on it, as do some of the pipes. The apparently steel hardware on the stainless steel clamps is also rusty and starting to corrode. The one piece I expected rust on, the steel ends that I welded the flange onto to mate to the exhaust headers, does indeed have obvious rust. Admittedly, I'm driving the car in winter (not much snow this year, but they still salt the roads), and completed two 2.5 hours highway trips a couple of weeks ago, but that still seems a bit fast -- the car has been on the road for under a month and a half.

    -- Joe

    IMG_0742.jpg

  9. #19
    Owner since 2007 Farrar's Avatar
    Join Date:  May 2011

    Location:  Fort Lauderdale

    Posts:    4,581

    My VIN:    02613

    Club(s):   (DCF)

    Joe, your exhaust interests me because I also have a 3.0L, but I have two Borla Pro XS mufflers rather than one dual. Near 2,500 RPM or so I have a pretty bad drone - one note that permeates quite strongly. But I haven't been able to document just how loud it is.
    DeLorean status: Replacing radiator and condenser.

  10. #20
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    696

    My VIN:    767 (3.0L EFI/EDIS)

    The Car Chemistry inserts might help with the drone. It seemed to help with mine, which was at about the same RPMs. JEGS has them for $57 each for the 2.5" with 3 discs (more discs means more silencing). You'll likely want a bench grinder handy so you can sand off the paint around the edges of the discs and a bit of the metal so that they'll actually fit in your pipes. You then rivet them in place (I used a magnet to find the discs), or run a bolt or wire through the pipe so they don't shoot out the back. While the CC guys say to install them before the mufflers but after the cats, you can install them after the mufflers as well. They just work best with hotter engine gases, but our exhaust is so short that there really isn't much of a run for them to cool down.

    I've attached some more pictures of my exhaust. As I mentioned before, the muffler hangs low so that the cats can run under the frame and body instead of being tucked inside of it closer to the engine, and to allow the use of pre-bent pipes. If you can bend the pipes, you can raise it up to more of a stock height. The pics sort of show the routing of the pipes, with the driver's side going through the "bottom" while the passenger side goes through the "top".

    I also realized that the amount of rust might be due to getting my engine tuned. I had this idea that I didn't need to put as much gas in the engine while decelerating (<30 MAP), so I leaned that way out. This seemed to introduce popping sounds in the exhaust at highway speeds when slowing down, which is apparently what happens when fuel burns in the exhaust instead of the engine. I did about two hours of continuous highway driving like this. Couple that with other over-lean problems I had due to a timing issue that caused the pipes and cats to glow while trying to get the engine idling mid last year, and it may simply be that the excessive heat ruined the anti-rusting properties of the stainless steel components. I'm going to replace the clamp hardware when I seal the exhaust in a few weeks.

    I've been wondering what would happen if I did set up the dual in/dual out muffler I'm using with the exhaust ports from the engine both going into the "top" and the tailpipes going into the "bottom". There is a 2" or so hole that connects the top and bottom chambers, so the exhaust should still leave the car. However, the exhaust ports from the engine would be firing exhaust basically directly at each other -- the hole to the bottom chamber would be a kind of side street that he gases can take. This would undoubtedly rob a fair bit of power from the engine, although I don't know if it would damage it or the rest of the exhaust system from the gasses having such an indirect exit. I imagine the car would run quieter, though. I just don't want to damage something finding out.

    Also, a correction: I'm running Magnaflow stainless steel cats, not Walkers; I had Walkers, but replaced them because the Magnaflows were SLIGHTLY shorter and allowed the exhaust to fit just a little bit better.

    Someday I'l get around to making a new bracket to level the exhaust out; it sits a bit low on the right at the moment.

    -- Joe

    From behind:
    IMG_0746.jpgIMG_0748.jpgIMG_0749.jpg

    Pipe routing (drivers side first, then passenger side)
    IMG_0753.jpgIMG_0750.jpg

    Tailpipes
    IMG_0754.jpgIMG_0755.jpg

Page 2 of 3 FirstFirst 1 2 3 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •